The rate at which at least one true null hypothesis is rejected

0.994.

Explanation:

Null hypothesis: In statistics, the term "null hypothesis" is described as a default position or a general statement that determine that there's no relationship that exists between two different measured phenomena as well as no connection between different groups.

If α = 0.05, then it represents five "true hypothesis" to get rejected whereas if each test is considered as mutually independent, then the "probability" of at least one "true null hypothesis" would be considered as rejected and is given by "1 − 0.95100 = 0.994".